Gantry scrapers of various designs are known for the clearing of heaps or dumps which are equipped with at least one swingable scraper jib. The gantry scrapers designed as high-efficiency equipment of modern construction have, in most cases, a scraper jib whose jib-length is approximately the same as the width of the dump, so that the entire cross section of the dump can be swept over with the scraping jib (U.S. Pat. No. 3,557,934). Since the scraping jib protrudes here relatively far beyond the gantry, in the upper swinging range of the jib, these gantry scrapers can, as a rule, not be used in roofed-in dumps or in halls or sheds, respectively, because of lack of space. True enough, there is a possibility to use, instead, gantry scrapers with so-called jointed or buckling jibs which can also clear the waste dumps along its entire cross section, without having the buckling jib protrude beyond the gantry and thus require a sufficiently large free space above the gantry (U.S. Pat. No. 3,814,268). However, such gantry scrapers equipped with buckling or articulated jibs constitute comparatively expensive equipment whose construction costs are also high.
If the gantry scraper is equipped with a rigid scraper jib whose length is smaller than the base width of the dump, the building containing the storage pile or the roof over the dump does not have to be constructed unnecessarily high. However, in this case, the scraper jib cannot sweep over the entire cross section of the dump; consequently, a residual heap remains on the side of the dump which lies opposite the swing pivot of the scraper jib; this residual heap cannot be cleared by the scraper jib. In most instances, the loss of the utilizable cross section is acceptable. However, the disadvantage lies mainly in the fact that most of the bulk materials no longer flow freely after their storage, so that dump-overhangs, i.e. so-called cornices, form in the area of the dump which is beyond the reach of the scraper jib. These cornices can reach considerable heights, particularly if the bulk material is moist and has a tendency to stick. Thus they may cause serious damage to the gantry scraper and its scraper jib if they suddenly collapse. In order to take remedial measures, it is known to equip shed service scrapers with special clearing devices, such as rigid harrows for instance, which clear the bulk material outside the swinging range of the scraping jib. (German AS No. 14 56 778). The known clearing devices are relatively heavy, expensive to construct and require a lot of space.